Gov. Jerry Brown is going to give Californians one last chance to make his impossible budget work. What’s less clear is what he’ll do if, as seems likely, they refuse.

Brown wants voters to OK a huge tax hike on Election Day. If they balk — as they have at the last two tax-increase propositions — he says he’ll have to slash $6 billion from the public schools and state universities, and shorten the school year by three weeks.

Proposition 30 would raise income taxes on Californians earning more than $250,000 from 10.3 percent to 13.3 percent for seven years. Over the same period, it would also boost the sales tax by a quarter of a cent — which would give California the nation’s highest state sales tax. In Los Angeles, the sales tax would top 9 percent.

Tax hikes are a rotten longterm strategy. As a new study by the Manhattan Institute shows, 3.2 million Californians have fled the state over the past two decades in search of lower taxes and a more reasonable cost of living.

And even Brown admits his plan would make California’s “revenue volatility” worse — that is, that the state relies too much on a small, fluctuating population of rich people to generate the bulk of its tax receipts.

But Brown says he needs this $8 billion in “temporary” new taxes to balance the state’s $91.4 billion budget — indeed, the “balanced” budget he passed earlier this year assumes the revenue.

Yet the ugly not-so-secret is that Brown needs the cash because he won’t keep state spending in check. His budget hikes outlays 7 percent over the prior fiscal year. That’s Golden State government-as-usual: From the 1991 budget to 2009’s, state spending grew an average of 5.37 percent a year, or roughly double the rate of inflation.

But Brown ran for governor promising not to force a tax hike “without a vote of the people.” Not that he has much choice: The state Constitution requires a two-thirds vote of both legislative houses, and he’s two Democrats short of the needed supermajorities in each house.

On the other hand, the constitution also requires a balanced budget — and the budget Brown signed into law in June found “balance” only via some far-fetched assumptions.

And not just that the voters would buy the tax hike. It also bet that capital-gains taxes from the Facebook IPO would generate $1.5 billion for the state treasury. Oops: Facebook stock’s down 40 percent. Now state officials hope booming iPhone 5 sales can fill the Zuckerberg gap (but those are slower than hoped, too).

Meanwhile, the odds are sinking for Prop. 30, despite Brown’s dire pronouncements. In the latest Field Poll, 51 percent of likely voters say they’d vote for the measure — down from 54 percent in July.

One problem is doubt that the money would be spend wisely. After all, Brown’s pushing ahead with his $68 billion high-speed train to nowhere.

Many Californians also figure the state could get by by raiding some of its secret cash stashes. In June, the state Parks Department found $54 million it had “misplaced” in a special fund.

That was twice the amount of money the Legislature cut from the parks budget this year — cuts that had state officials threatening to close 70 parks from the desert to the sea by July 1. Brown’s glib response at the news: “Hallelujah! More money is better than less money.”

If the Parks Department had $54 million socked away, how much do other state agencies have stashed? Official estimates run between $8.8 billion and $11 billion — more than Prop. 30 would yield.

On the other hand, Brown might just find a way to hike taxes without Prop. 30, if Democrats can pick up those four legislative seats in November. Earlier this month, he told the editors of The San Francisco Chronicle that if Prop. 30 loses, “we’re not going to go out to the people again. Because we’ve triedit.”

The voice of the people is the voice of God — until the people say no. If Democrats win two-thirds of the state Senate and Assembly in November, the voice of the people won’t count for much.

Southern Californian Ben Boychuk is an associate editor of the Manhattan Institute’s City Journal.